The concepts of coordination and cooperation are widely used in economics, and particularly in game theory. They were also at the foundation of development economics at the time of WWII, with Paul Rosenstein-Rodan highlighting the existence of intersectoral spillovers effects, multiple equilibria and underdevelopment traps. These concepts returned to the forefront of development theory in the 1970s with the notions of coordination failure and poverty traps, as well as the research on social norms. One example was Samuel Bowles’ seminal concept of ‘institutional poverty traps’, i.e. highly inegalitarian institutions that persist even though they are inefficient. Membership institutions are of particular relevance in developing countries, and therefore in development economics. The paper explores the cognitive dimensions of coordination failures and institutional traps; it reveals that local institutions in developing countries may be efficient and examines the conditions in which norms create poverty traps, in particular membership norms. Firstly, it is argued that institutions and norms are key causes of the formation and persistence of poverty traps. Institutions and norms are complex cognitive devices, some beliefs and norms appear to be particularly resilient and difficult to revise. Secondly, it is shown that no particular institutional form is ex ante a cause of poverty traps: depending on contexts, the same institutional forms can be efficient or inefficient. It is the combination of multiple elements – economic and political environment, and social norms - that create thresholds effects and entrap groups into low equilibria. Thirdly, it is argued that the norms that organise group membership, because they involve beliefs that are difficult to revise, are typical factors of poverty traps.